Welcome to Vodafone Community
Apologies for the delay in responding. If you're currently in an IOU you'll just need to top up to clear the IOU as Cookie has suggested & you should then be able to change your top up offer. If you have cleared the IOU amount but are still unable to change your offer can you send us a private message (via the link in my signature) & we can take a look into this for you?
Date of birth: